There is one thing in common with all newbies: they only shoot up the middle.
So then the best games for newbies are ones where constantly shooting up the middle will cause something interesting and meaningful to happen.
Doctor Who, is probably the best I've found that is like this. Players can simply keep shooting up the middle and get the multiball. All up the middle they can: shoot locks, wail on some targets, shoot into dalek gates, and watch the balls fall towards you for multiball.
I also have Road Show, which you'd think is similar: shoot up the middle and wail on Ted's dozer blade, then shoot the locks to start multi ball. But newbies simply cannot make the lock shot required to start it — it's a tough shot.
WCS is a good one, getting goals is fun for everyone.
Another good one is Junk Yard. Wailing on the wrecking ball and shoot up the middle to start multiball is really fun for newbies too.